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Art & Science of Composting
 By Patty Kleinberg, Director of Education, Queens Botanical Garden
Need a quick review? Here are the basics to understanding the composting process.
Composting is a natural process. Organic matter such as leaves, grass clippings, plants, paper, and woodchips decompose or break down by the action of living microscopic organisms. Think about it: if this natural process didn’t happen, the forest floor would have filled up by now. By controlling this process, in other words, creating the ideal conditions for the microbes to flourish and do their work, we can make compost more efficiently and faster than nature can alone.
The microbes we want working for us in a compost bin or pile are the ones that breathe oxygen. These aerobic microorganisms, like us, need water and nutrients in order to survive and reproduce. These nutrients come from the organic matter that is added to the compost bin or pile. The water is found naturally in plant and food waste but sometimes we need to add more. The two primary nutrients for the microbes are carbon and nitrogen. The carbon provides food energy, similar to carbohydrates for us human organisms. The nitrogen provides protein for reproduction and synthesis of new cells.
All organic matter is made of these two ingredients—carbon and nitrogen. We usually refer to the carbon to nitrogen ratio or C:N of the material. Materials high in carbon have C:N ratios of 30:1, 200:1, etc. These high carbon materials tend to be dry and brown, such as fallen leaves. Materials considered high in nitrogen will have a C:N ratio like 2:1, 10:1, etc. These materials tend to be wetter, such as grass clippings. Materials high in nitrogen also can get quite “stinky” if not properly composted.
Microbes prefer a diet high in carbon with just enough nitrogen for overall health. We like to see a total ratio of 30:1 as a starting point for adding material. But you should not need a C:N table. Simply ensure that for every handful of high nitrogen (potentially stinky) material you add to the bin, you also add at least two handfuls of dry, carbon materials, such as fallen leaves or shredded newspaper.
Monitor moisture levels to keep those hardworking microbes happy. The consistency of a wrung-out sponge is what you’re trying to achieve. Be aware that the outer edges will dry out more quickly and dry pockets can develop inside the system. Try to fluff or turn the composting material as you’re adding water for more consistent moisture levels throughout the pile. Remember, too much water is not good. Excess water will fill the air spaces, forcing out the oxygen these microbes need to survive.
The heat that is generated in a compost pile is due to the activity of these microbes. If for some reason the microbe population dies back due to a lack of adequate moisture, oxygen, or proper nutrition, you will not feel the heat. If this is the case, determine what caused the dieback and correct the situation. For example, too much water means not enough oxygen. Turn the material to aerate and add dry leaves or shredded paper if necessary.
The important thing to remember is this: keep those microbes happy and the rest will take care of itself.
Happy Composting! |
